1. Field of the Invention
The present invention relates to an optical switch, and particularly to an optical switch employing a piezoelectric element to perform optical switching function.
2. Description of Related Art
With the increasing development of optical telecommunications, the development of optical switches has become vital for better performance. A typical optical switch has one or more light input port(s) and at least two light output ports. Using these ports, the switch performs switching or logical operations on optical signals in a light transmitting link/system or in an integrated optical circuit. Measures for assessing the capability of an optical switch include low insertion bss (IL,  less than 1 db), good isolation performance ( greater than 50 db), and fast switching speed (normally, tens of milliseconds).
Optical switches are commonly catergorized into mechanical type and non-mechanical type. In principle, a mechanical type optical switch has a number of advantages over a non-mechanical type optical switch when switching speed is not a critical factor for performance consideration. The mechanical type optical switches offer low insertion losses, high degree of immunity against backscattering of light from the switch back down the input fiber, low cross-talk, and insensitivity to wavelength of light.
Some conventional mechanical switches operate by moving an input fiber relative to a plurality of output fibers. Examples of such designs are disclosed in U.S. Pat. Nos. 4,303,302, 4,896,935 and 5,175,776. However, these optical switches share a common problem. They require high precision parts to obtain precise positioning control and low insertion loss. This results in high cost and complicated manufacturing process. Moreover, moving fibers repeatedly to and fro is apt to damage or even break the fibers.
Other kinds of conventional mechanical optical switches perform their optical switching functions by moving optical elements of the switches, such as ferrules with attached input/output fibers, reflectors, and lenses. U.S. Pat. No. 4,261,638 discloses an optical switch as shown in FIG. 5 of the attached drawings, comprising a rotatable reflector 3. The switching function is performed by rotating the reflector 3. The reflector 3 can be rotated around different axes, such as axis 2-2xe2x80x2, to switch the transmission of light coming from an input fiber 1 between selected output fibers 6. The switching speed of this optical switch is determined by the rotating speed of the reflector 3 and corresponding controlling mechanisms of the reflector 3. Since the optical switch is operated by rotating the reflector 3 around different rotating axes, the design and manufacturing of the optical switch are complicated. resulting in high cost.
A main object of the present invention is to provide an optical switch with high switching speed and low insertion loss.
An optical switch in accordance with an embodiment of the present invention comprises an input port and first and second output ports. An optical switching subassembly is arranged between the input port and the output ports. The input port and the first and second output ports are arranged in a T-shaped configuration with the input port and the second output port substantially aligned with each other forming an optical path. The first output port is arranged perpendicular to the optical path. The optical switch further comprises a shell enclosing the input and output ports and the optical switching subassembly.
The optical switching subassembly includes a first optical transmitting medium and a second optical transmitting medium respectively having first and second surfaces spaced from and opposing each other. A switching means is movably retained between the first and second surfaces of the transmitting media. The switching means comprises two optical transmitting liquid sections between the surfaces and an air section between the liquid sections. A piezoelectric (PZT) element is in physical engagement with one of the liquid sections and can be electrically biased to move the switching means between first and second positions.
The first and second optical transmitting media have the same first refractive index N1. The first and second transmitting liquid sections have the same refractive index N2 which is approximately equal to N1.
When the switching means is at the first position, the air section is coincident with the optical path between the input port and the second output port. Thus, light from the input port will be fully reflected by the first surface of the first optical transmitting medium and re-directed to the first output port. When the switching means is at the second position, the air section is moved out of the optical path and one of the liquid sections is moved to the optical path between the input port and the second output port. Since the second refractive index N2 is approximately equal to the first refractive index N1, light from the input port is transmitted directly through the first transmitting medium, the liquid section and the second transmitting medium, and exits the optical switch via the second output port.